Over the years, various systems have been devised for controlling engine-driven fire pumps. For instance, U.S. Pat. Nos. 3,786,689 A and 4,189,005 A to McLoughlin, as well as U.S. Pat. No. 5,888,051 A to McLoughlin et al., disclose apparatus and methods for controlling the pressure output from engine-driven centrifugal fire pumps. U.S. Pat. No. 7,040,868 B2 to McLoughlin et al. discloses systems for controlling pumping speed during discharge pressure fluctuations. U.S. Pat. No. 8,517,696 B2 to Mcloughlin et al. discloses a system for maintaining the fluid intake pressure of a pumping system above a preset value, while U.S. Patent Application Publication No. 2005/0061373 A1 to McLaughlin (sic) et al. discloses a system for maintaining the fluid intake pressure below a preset value.
One disadvantage of pump pressure governors that only control discharge pressure is that they are often unresponsive, or too slow to respond to, sudden pressure changes at the intake end of the system. Also, these types of governors are not able to reduce extremely high incoming pressures—for instance, pressures of 200 psi or higher—to a safe discharge pressure of approximately 100 psi. In addition, these types of pressure control systems do not include any backup mechanisms for controlling the discharge pressure if the pump governor should fail.
The system disclosed in aforementioned U.S. Pat. No. 8,517,696 B2 to McLoughlin et al., which maintains the intake pressure above a preset value, is more effective at responding to sudden pressure drops than systems which control discharge only, but it is not designed to control sudden pressure increases, or to control the discharge pressure if the pump governor fails. Conversely, the system disclosed in U.S Patent Application Publication No. 2005/0061373 A1 to McLaughlin (sic), which maintains the fluid intake pressure below a preset value, is not designed to respond to sudden pressure drops or for use with non-pressurized fluid sources.
In addition, the intake pressure control systems disclosed in both U.S. Pat. No. 8,517,696 B2 to McLoughlin et al. and U.S Patent Application Publication No. 2005/0061373 A1 to McLaughlin (sic) require the presence of a reserve tank (in addition to the onboard supply reservoir carried on a fire truck), wherein excess flow is diverted to the reserve tank when the intake pressure is too high, and/or liquid from the reserve tank is added to the flow in the intake conduit when the intake pressure is too low. The reserve tank and its associated piping add weight to the fire truck and increase the overall complexity of the system, making it time-consuming to set up and take down.
Accordingly, there exists a need for an intake pressure control system that can operate effectively under high flow, high pressure conditions, as well as low flow, low pressure conditions; can respond quickly to sudden pressure drops and increases regardless of whether the fluid source is pressurized or unpressurized; and do not require the presence of a reserve tank.